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Session: Advances in Intraplate Earthquake Geology

Type: Oral

Date: 4/24/2019

Time: 09:30 AM

Room: Vashon

Quaternary Geologic Mapping and Paleoseismic Assessment of the Warm Springs Valley Fault, Washoe County, Nevada

The northern Walker Lane, in western Nevada, is a region of distributed deformation that accommodates ~15% of the motion between the North American and Pacific plates along north-oriented normal faults and northwest-oriented strike slip faults including the Warm Springs Valley fault (WSVF). The WSVF extends ~70 km from the Warm Springs Valley to the Honey Lake basin. Previous studies on the northern section of the fault reveal a decreasing slip rate from 1.8-2.4 mm/yr in the late Pleistocene to 0.2 mm/yr in the Holocene; however, information on earthquake timing, recurrence and Holocene activity is poorly constrained. Here, we present preliminary results of Quaternary geologic mapping and a paleoseismic trench investigation on the WSVF. The goals of our study are to locate the distribution of active traces and characterize the faults earthquake history. Mapping observations indicate that the fault is characterized by (1) a single trace in Warm Springs Valley, (2) multiple parallel stepping and anastomosing fault strands, uphill and downhill facing scarps, push up mounds, and sag ponds between the Dogskin and Virginia mountains, and (3) a range front fault along the Fort Sage Mountains that steps to the east and cuts pluvial lake shorelines in the Honey Lake basin. A trench excavated across a 3 m downhill facing scarp on an alluvial surface revealed sandy alluvium on the footwall juxtaposed against red gravel and colluvial deposits on the hanging wall. A weakly developed soil with stage 1 carbonate filaments is cut at the fault and indicates the surface is latest Pleistocene in age. Based on stratigraphic relationships, we infer that at least two surface rupturing earthquakes have occurred along the WSVF since the latest Pleistocene, the timing of which will be evaluated with OSL and radiocarbon analyses. Evaluation of offset shorelines in Honey Lake basin is in progress and will provide a better constraint of the Holocene slip rate for the WSVF.

Presenting Author: Colin M. Chupik

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